The invention relates to a circuit arrangement for reducing noise when peaking the edges of a useful signal by combination with a peaking signal derived therefrom, which signal only influences the useful signal when a predetermined amplitude threshold is exceeded, said arrangement comprising a peaking signal stage for supplying the peaking signal and a noise suppression stage in which a noise suppression signal is generated and is superimposed on the peaking signal, the peaking signal stage applying the peaking signal to two push-pull current outputs.
A circuit arrangement for reducing noise is known from U.S. Pat. No. 4,536,796, particularly FIG. 3 and the associated description, which circuit arrangement forms a peaking signal from a video signal via a linear differential amplifier and a so-called coring signal via a two-stage limiter amplifier. The signal, which is designated as peaking signal and is applied to two push-pull outputs by the linear differential amplifier, is superimposed with the coring signal forming a cored-peaking signal which is subsequently combined with the video signal.
A circuit arrangement for processing a colour video signal comprising an arrangement for correcting definition is known from DE-PS No. 31 36 217. In this circuit arrangement a sub-signal is formed from the luminance signal of the colour video signal and it is added to the luminance signal for the purpose of correcting the definition. The definition correction does not become effective until the sub-signal exceeds a given minimum amplitude value determined by the adjustment of a threshold device. This device is represented by an amplitude-dependent controlled amplifier whose gain factor is substantially zero until the threshold value has been reached and which then assumes a finite value.
In arrangements for correcting definition, also referred to as aperture correction circuits, the amplitudes of the signal component having a higher frequency are raised to a higher value than those of the signal components of a lower frequency. Consequently, steeper signal edges are produced, which results in an improved picture definition, for example, in the video signal. Naturally, the amplitudes of noise signal components are also raised when generating the sub-signal. Particularly low-frequency video signal components having a small amplitude, such as occur in the display of uniform picture areas, have a noticeably poorer quality if they are beset with noise. The said threshold device counteracts this in that it suppresses noise signal components up to the amplitude threshold in the sub-signal.